The present invention relates to the efficient and reliable transmission of packet or cell-based information, such as frame relay, SS#7, ISDN, Internet or asynchronous transfer mode (ATM) based information, via wireless (terrestrial or satellite) telecommunication network. The techniques and the resulting wireless network are applicable to both terrestrial and satellite wireless environment and is particularly applicable to an Asynchronous Transfer Mode (ATM) network or frame relay network, although the application to other networks having cell or packet transmissions would be understood by one of ordinary skill in the art without undue experimentation. Although the examples of the applicability of this invention are drawn mostly to an ATM satellite communications network, it would be clear that the underlying invention is applicable to other cell and packet systems.
The implementation of the invention results in a mesh heterogeneous satellite network with the following major characteristics:
Single satellite hop connectivity among terminals of widely varying capabilities (uplink rates varying from 8 Kbps to 8 Mbps); and
Simultaneous Multimedia/Multiservice Communications Sessions from a terminal with multiple destinations via a single modem and a single uplink and downlink chain.
While the present discussion uses Asynchronous Transfer Mode (ATM) transmission by way of example to define the problems with conventional bandwidth on demand systems, this invention is not limited to ATM systems. Distinct advantages are available in other transmission systems, including those based on frame relay, Internet and ISDN/SS#7 protocols, when this MCDD architecture is implemented. Problems with conventional ATM and advantages of the present invention are presented in detail, but one of skill in the art would understand that these advantages would also benefit other transmission schemes such as ISDN, Internet and SS#7.
ATM is a transmission and switching technology which has been standardized to carry statistically multiplexed traffic of different kindsxe2x80x94voice, date, and video. The bandwidth requirements for ATM traffic varies with the fluctuations in the user generated traffic, which can vary over a wide range. Also, the traffic generated from a particular source could be intended for a number of geographically dispersed destinations.
These salient features of ATM traffic demand simultaneous connectivity from a source to multiple destinations. The bandwidth requirements for each of these connections can vary widely.
The traditional Frequency Division Multiple Access (FDMA) (either single channel or multiple channels per carrier) method to provide single hop wireless and satellite ATM mesh connectivity among several terminals is very impractical for the following reasons. Simultaneous connectivity among multiple terminals needs a bank of modems and a number of uplink and downlink chains making the system very expensive. Also, the ATM cell transfer delay becomes large for the lower rate carriers, even though the terminal may be transmitting at a much higher aggregate rate.
The traditional Time Division Multiple Access (TDMA) or the enhanced multi-frequency (MF) TDMA systems work well at high rates (e.g. 2 MBPS or higher). However, an MF-TDMA system is not efficient if the carriers are of widely different rates of lower speeds (e.g. 8 Kbps) and higher speeds (e.g. 2 Mbps or 8 Mbps) which need to be considered together as a whole system. Considering that ATM is a scalable technology and that a terminal may be capable of transmitting at only low rates, such as 8 Kbps, to an MF-TDMA system cannot handle ATM traffic from such terminals in an efficient-manner.
Bandwidth on demand is typically achieved in the MF-TDMA system by a separate channel (a time slot on a frequency) from each terminal to a Network Control Center (NCC). According to the present invention, a request for bandwidth can be multiplexed with the traffic on any existing transmitting carrier, thereby reducing the requirement for a request channel considerably. Furthermore, since the bandwidth request can be received by all terminals, a distributed bandwidth allocation algorithm can be easily implemented.
In an MF-TDMA system, traffic from a terminal to multiple destinations is carried in different time slots with different rates. Thus, the traffic at lower rates suffers greater ATM cell delay. According to the present invention, the traffic from a terminal to different destinations can be multiplexed and aggregated on a larger carrier thereby reducing the ATM cell delay.
Finally, the satellite environment leads to a number of major challenges in the ability to provide satellite-based ATM services. These challenges stem from the fundamental differences in the satellite/wireless and fiber environments and from the fact that the ATM network architecture and protocols are designed for fiber optic cable infrastructure.
Specific problems arise because of three inherent characteristics of satellite linksxe2x80x94(a) errors, (b) delay, and (c) bandwidth limitations, as discussed in D.M. Chitre, D. Gokhale, T. Henderson, J. Lunsford and N. Mathews, 1994, xe2x80x9cAsynchronous Transfer Mode Operation Via Satellite: Issues, Challenges and Resolutionsxe2x80x9d. International Journal of Satellite Communications, Vol. 12, pp. 211-222.7.
Satellite RF links have considerably degraded error performance with respect to fiber optic links. For example, ATM protocols assume that a transmission medium has a very low Bit Error Ratio (BER)(10xe2x88x9212) and that bit errors occur randomly. In contrast, the bit error ratios associated with terrestrial wireless and satellite communications are much higher (on the order of 10xe2x88x923 to 10xe2x88x928) and tend to fluctuate with atmospheric conditions.
In addition, in satellite systems, typical forward error corrected satellite links will have bursty errors with variable error rate as opposed to random errors on the fiber links. ATM operation is intolerant of burst errors, and the ATM quality of service requirements for multimedia applications are much more stringent than what a typical satellite link will provide. The one-way propagation delay of around 250 msec., which is intrinsic to geosynchronous satellite communications has an adverse impact on the data communication protocols, such as TCP at high speed (fractional T1 or more), and on the ATM traffic and congestion control procedures.
Furthermore, satellite bandwidth, and terrestrial wireless bandwidth to a lesser extent, is a precious asset. Thus, the cost of bandwidth in a wireless network is much higher than in a fiber optic network. Thus, wireless systems tend to be unable to accommodate the bandwidth inefficient operation of ATM protocols. For example, ATM constant bit rate (CBR) speech will require a 70 kbps satellite bearer channel to carry one voice channel. As a result, the onus is on the operator of a bandwidth limited network to either tolerate the bandwidth inefficiencies of ATM technologies or to design special signal processing equipment that reduces the overhead across a bandwidth constrained network path. Therefore, if ATM technologies are to be implemented in wireless networks, more efficient bandwidth utilization schemes must be achieved, as in the present invention.
Current methods for bandwidth on demand/ATM products rely on the TDMA multiple access technique. Single carrier TDMA is not an attractive solution for bandwidth on demand/ATM because the amplifiers at the user transmitting stations must be sized for the peak power, which is much larger than the average power for single carrier TDMA. This is in addition to the additional complexity usually associated with the synchronization requirements of TDMA.
Traditionally, the selection of the multiple access scheme for ATM transmission over satellites is largely based on tradeoffs such as space segment efficiency, cost and complexity of earth stations, and single versus multiple carrier operation, where multiple carrier operation results in necessary amplifier backoff. In traditional FDMA systems, a bank of filters and modems are used. Advances in digital processing have made possible a more attractive multicarrier demultiplexer/demodulator (MCDD) implementation, which allows the flexibility of having different size user stations in the terrestrial wireless or satellite network. Cost savings in the baseband and RF equipment can be realized for the smaller stations which handle only a fraction of the traffic that the larger stations can handle.
The present invention concerns an apparatus and method applicable to a terrestrial wireless or satellite communication system with a plurality of user stations, wherein bandwidth on demand service is provided to each user station by dividing a selected bandwidth into a plurality of frequency subdivisions and assigning a number of the frequency subdivisions to an individual user station in the wireless or satellite communication system. The number of frequency subdivisions assigned to each user station is maintained to be commensurate the volume of transmission traffic of each user station by changing said number of frequency subdivisions assigned to each individual user station as the volume of transmission traffic of each individual user station changes.
The frequency subdivisions may be of equal or unequal size. In one embodiment, the frequency subdivisions are of equal size, and any newly added frequency subdivisions are adjacent to previously assigned frequency subdivisions.
In a second embodiment, one unequal size frequency subdivision is assigned to a user station, where the size of the frequency subdivision assigned satisfies the current transmission needs of the user station. When the user station transmission requirements change, a new frequency subdivision of the size to satisfy the new transmission requirements replaces the previously assigned frequency subdivision.
A hybrid architecture where some terminals transmit in single carrier mode while other terminals transmit in multiple carrier mode is also within the scope of the present invention.
As used herein, the term xe2x80x9ccellxe2x80x9d shall be used to mean a fixed size container, such as the ATM cell, and As the term xe2x80x9cpacketxe2x80x9d shall be used to mean and a variable size container, and the term xe2x80x9ccell/packetxe2x80x9d shall mean generically either or both such container arrangements.